What are Sunspots and How are Sunspots Formed?


Sunspots are temporary phenomena that occur on the Sun’s photosphere which appear as spots darker than the areas surrounding it. These regions reduce the surface temperature which are caused by concentrations of magnetic field flux and inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity. The numbers of these sunspots vary per year.

A sunspot is a place on the surface of the Sun that has a cool temperature and an intense magnetic field. They are also magnetic structures that appear dark on the solar surface. One major reason why sunspots appears to be black on the earth surface is that the average temperature of the surface of the Sun is about 10,000°F, and the average temperature in the center of a sunspot is 6400°F.

Groups or individual sunspots may last from a few days to a couple of months but in the end, they eventually decay. Sunspots contract and expand as they move across the Sun’s surface with diameters reaching as much as a hundred and sixty thousand (160,000) kilometers. These sunspots may travel at proper motions or relative speeds starting at a few hundred meters per second upon emerging.

Sunspots produce magnetic activity which is quite significant and strong, they are also accompanied by secondary occurrences such as reconnection, prominences and coronal loop events. Most coronal mass ejections and solar flares originate in a region that is magnetically active encompassing visible sunspot groupings. Similar phenomena observed on stars and other suns are accompanied by another phenomena called starspots.

Although temperatures of sunspots range from 3,000 to 4,500 K, the contrast with the surrounding material which is about 5,800 K leaves these sunspots clearly observable as dark spots. This is because the brightness of this visible light of a heated black body in close approximation by the photosphere at these temperatures varies greatly with temperature – considerably more compared to the total black body radiation emitted by the Sun. Sunspot have two major parts, the umbra which is the darkest part of the sun bearing a vertical magnetic field and the penumbra which is the lighter part bearing an inclined magnetic field.

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Sunspots have a tendency to appear in magnetically bi-polar groups. In each group there are normally two major spots, oriented approximately east-west, called the leading, preceding or western, and the following or eastern spot. The leading spot is usually larger in size and has stronger magnetic field strength. It is first to form, first to develop penumbra, and last to dissipate.

Sunspots may last from a few days to a few months but eventually they disappear. They contract and expand as they move across the Sun’s surface and though the details of sunspot generation is still a debate, it seems that the visible counterparts of magnetic flux tubes in the Sun’s convective zone are amalgamated by differential rotation. If the stress on these tubes reach a certain point, they curl up and eventually puncture the Sun’s surface. Convection is inhibited at these puncture points; the energy flux from the interior parts of the Sun decreases along with its surface temperature.

The Wilson Effect states that sunspots are depressions on the Sun’s surface. The Zeeman effect, on the other hand, show that prototypical sunspots come in pairs with contrasting magnetic polarity. In each cycle, sunspots change from north to south and from south to north and back. They appear in groups.

Magnetic pressure tends to remove magnetic field concentrations causing the sunspots to dissipate but the lifetime of these sunspots are usually measured in days to weeks. In the year 2001, observations from SOHO or the Solar and Hellospheric Observatory using sound waves traveling beneath the photosphere were used to develop 3D images of the internal structure under sunspots; these remarks portray a powerful downdraft below each sunspot which forms a rotating vortex that could sustain the concentrated magnetic field.

Sunspot cycles transpire about every eleven (11) years with some variation in length. In a solar cycle, sunspot populations rise very quickly and fall at a slower rate. The point of the highest number of sunspot activity in a cycle is known as the solar maximum. On the other hand, the solar minimum is the point of a sunspot’s lowest activity.

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At the early stages of the cycle, sunspots appear in the higher latitudes of the sun and then move towards the equator as the cycle reaches the maximum, this is according to Sporer’s law. Sunspots that come from two adjacent cycles can exist simultaneously for a specific period and can be distinguished by the magnetic field that they possess.

In order to count the average amount of sunspots and groups of sunspots during intervals, the Wolf Number Sunspot Index is used. This eleven (11) year solar cycle are each numbered sequentially and observations using the Wolf Number Sunspot Index have begun since the 1750s.

It was George Hale who first linked magnetic fields and sunspots in the year 1908. He suggested that the sunspot cycle period is about twenty-two (22) years which covers two periods of decreased and increased sunspot numbers which are accompanied by polar reversals of the magnetic dipole field. Soon after, it was Horace Babcock who proposed a qualitative model for the dynamics of the Sun’s outer layers. This model explains that these magnetic fields are caused by behavior described by Sporer’s law.

Sunspots are connected with solar events such as coronal mass ejecctions and flares. A solar flare is the sudden release of energy from thhe Sun and while coronal mass ejections actually shoot hot plasma to space their precise mechanisms are still unknown. Coronal mass ejections and flares can send gargantual amounts of charged particles and energy into collision with the Earth’s atmosphere where they can cause magnetic storms that disrupt cell phone and radio communication and affect electrical grids. During the 1989 event, the solar max, a power surge triggered by energy from the sun damaged several transformers that were part of the Hydro-Quebec power system. This power surge left about six (6) million people in Canada and the United States without electricity for over nine (9) hours.

The increase in solar radiation that occurs with solar flares is a health hazard to astronauts in space, passengers and crew in high-flying aircrafts but, there is a lack of evidence that proves that these people might have gotten sick from such exposures.

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Even until today, there are a lot of questions that arise between the link of changes in Earth’s climate and solar weather since Earth is influenced by several factors which include greenhouse gases, volcanic eruptions and the link. The Maunder minimum in the 1600s was the time when almost no sunspot activity occurred. In this time, Earth experienced cold temperatures and severe temperatures in North America and Europe.

It was ancient Chinese astronomers who first noticed sunspots nearly a thousand years ago. The Book of Changes, which dates back to 11th BC, states that a star was seen within the sun. The first written record of sunspot sighting dates back as early as 28 BC when it was noted that the sun was yellow and a black vapor as large as a coin was observed at the center.

After the telescope was developed in the 1600s, Galileo and his colleagues observed that the sun had dark spots. Catholic and Astronomer Christoph Scheiner attempted to come up with an explanation that didn’t contradict the Church’s teachings and argued that these spots were actually undiscovered planets that revolved around the sun at close proximity which were visible only when the planets were in front of the sun. Galileo, however, correctly figured out that sunspots were part of the sun itself by closely observing the movement of sunspots over time and by the mid 1700s, European astronomers were compiling and recording their observations on the Sun’s sunspots on a daily basis.

Since the 1900’s, scientists have used an array of tools which include giant solar telescopes that were specially develop to observe the sun’s light without being distorted by the heat it emitted. Astronomer George Hale then discovered the magnetic nature of sunspots and used his discovery to prove the existence of magnetic fields in the interior of the Sun.

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